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        # Window Profile Extrusion: Getting the Surface Finish Right

        

**Topic:** Rigid PVC

        

Your UPVC window profiles have a rough, matte surface with visible flow lines. The customer wanted a mirror-smooth, glossy finish. Your entire batch sits in the warehouse, unsellable.

        
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## Problem

Surface defects in profile extrusion stem from three main causes: poor melt quality (unmelted resin particles or 'fish-eyes'), incorrect lubricant balance (causing drag marks or die lines), and sub-optimal die design. The melt needs to be perfectly homogeneous and flowing at precisely the right viscosity when it exits the die. Too hot, and you get thermal degradation; too cold, and the surface goes rough.

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## Likely cause

This issue often stems from inconsistent compounding temperatures, inferior raw material purity, or unbalanced stabilizer ratios within the formulation matrix.

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## Corrective direction

The foundation of a good profile is **NBT SG-5 resin (K-67)** with its uniform particle size for rapid, complete fusion. The lubricant system must be precisely balanced: **Calcium Stearate** (internal) provides melt flow, while **PE Wax and Oxidized PE Wax** (external) control die release and surface gloss. NBT recommends a **Ca-Zn stabilizer system** for the best initial color in white profiles. Critical additional step: ensure your die temperature has a **2-3°C gradient** from the body to the lips, with the lip slightly cooler to set the surface before it exits. Our technical team provides free die-setup consultations for profile manufacturers.

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          ## Frequently Asked Questions

          
### What's the ideal melt temperature for profiles?

For white UPVC profiles, target 185-195°C at the die exit. Monitor with a melt probe, not just the barrel zone setting.

### How important is the calibrator in surface finish?

Critical. The vacuum calibrator must pull the profile firmly against the sizing plates. Insufficient vacuum = wavy surface.

        
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By NBT Technical Desk · Updated 2026-06-07

        

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